4th axis steady rest (DE: Lünette) for my CNC

Today I made myself a small steady rest for my CNC.
It's very easily 3D printed and intered specifically for milling.
This is because you push down on the part and only need to support the underside.
Also it mounts to the T-slot table of my YOOCNC 6040+Z using M6 bolts).

I did this because I am planning some very agressive milling and don't think that my tailstock alone will be enough to support the stock during roughing.


ATC choices

Project history

  1. Evaluating my choices in  back in February
  2. Decided on what ATC system to get in March. (posting contains MACH3 software references)
  3. The Usovo spindle and parts finally arrived in April
  4. Mounting spindle and cables in May
  5. Defining M06 tool change macro
  6. Next project: designing a chain link tool library

I'm thinking of upgrading my YOOCNC 6040 desktop CNC mill to an automatic tool change.
These are the options I'm evaluating:

Option 1


  • 2500eur
  • 27.600RPM
  • 700W (0.15Nm)
  • SK15-ER11 (tools up to 8mm)
  • 5xSK15 included, +60eur for additional ones
  • 1.5Kg
  • 0.01mm runout
  • can drive a pneumatic tool magazin.
  • needs 8 bar minimum (Mechatron pressure booster required)

Option 2

Mechatron Vorsatzwechsler

  • 1000eur
  • 24.000RPM max
  • existing 2.2KW spindle (up to 0.9Nm)
  • SK10(ER11+ER16) 
  • adds +1.7Kg to the existing 6Kg spindle
  • make the spindle too large and top-heavy for the gantry
  • needs 10 bar minimum (Mechatron pressure booster required)

Option 3

Can I get the ATC-8022-42 instead? (2.2Kw 42.000RPM, HSK25)  - 6500CHF -> too expensive
  • 3900eur
  • +150eur per SK20 toolholder 
    • runout < 2µm
    • or 50-60eur for ER16, ER20 and ER25(<=16mm) collets
  • +27eur per ER16 collet with low runout
    • +10eur per ER25 collet at Usovo
    • or cheap in China
  • 30.000RPM
  • 2.2KW (0.7Nm)
  • SK20-ER16 (tools up to 10mm)
  • SK20-ER20 (tools up to ??mm)
  • SK20-ER25 (tools up to 16mm)
  • 8Kg (+2Kg over the existing spindle)
  • has it all.
  • needs only 6 bar
The option to use cheap SK20 tool holders for drills and roughing tools and precise ones for finishing tools is quite interesting.

Option 4

Chinese spindle GDL80-20-30Z/2,2
  • 2400eur+customs+19% import sales tax = 2900eur + customs
  • 30.000RPM
  • 2.2KW
  • SK20 (15°)
  • 8Kg (+2Kg over the existing spindle)
  • needs only 6.5 bar


Apparently there are cheap 60.000 RPM spindles with no tool change.
Obviously for plastic and wax these would cut down a lot on milling time.


Do I need 2.2Kw to do the full 30.00RPM in POM, wax and soft wood?
700W should be enough but there is little reserve.

source: http://www.kimla.pl/en/HowtochooseaCNCspindle
Aluminum, plastic, wood or laminate with
cutters up to 5mm  - 0.8kW 24,000 rpm is sufficient,
cutters up to 8mm - 1kW spindle,
cutters up to 12mm - 3.3kW spindle

Steel: (15,000 to 18,000 rpm) cutters up to 10mm - 3.3kW spindle
cutters up to 12mm - 5.6kW spindle
cutters up to 16mm - 7kW spindle
cutters up to 20mm - 10kW spindle.

Drill in steel - more powerful spindle because
6mm drill at 2000rpm with the 5.6kW 18,000 rpm spindle

You cannot compare the powers of spindles with the powers of conventional milling machines because they have gears and there is no need to have such a torque reserve.

How much of a time difference are 24.000RPM vs 30.000RPM in the end?

What tools >8mm would I want to use? 
I could use 16mm instead of 10mm planers.


Slow progress on CNC upgrade

I'm currently doing a lot of upgrades to my YOOCNC 6040.
However every step takes at least twice as long as planned.

back access

My CNC mill is inside a wooden enclosure that keeps the chips from spreading all across the workspace and gives me a place on top of the machine for control box and power sockets as well as a place to attach the articulated touchscreen computer running MACH3 to.
To get to all the parts, I need access to, I had to cut a wide hole into the back of this enclosure.
(Particularly one of the cable chains runs down the back.)

Status: DONE

cable chain

As a first step I upgraded the cable chains. 
Because I would add a lot of cables for the end-stops, I wanted cable chains that can be opened up to access the cables within. However I ordered the wrong ones and they turned out to require too much of a bending radius. So I had to order different ones from Motedis.

Status: DONE

end stops

The first real upgrade are end stops.
I had the parts for these in the drawer for years but never got around to mount them.
There are these wonderful end stop mounts from David Ryan. However I soon found out that 2 of them required drilling holes into the machine.
So I designed improved ones that used existing screws and the T-Slots on the side of the work table.

Problem is, the Purelogic PLCM-B1 requires me to provide my own power for all inputs. 
Up to now I had a 5V wall wart style power supply hooked just for the tool height probe.
This required me to create an external box that would distribute and provide power for every input.


Beefy A axis

My old A-axis had a longneck stepper motor on a wobbly 1:8 XL belt.
The belt was the wrong kind to begin with (XL belts are for driving things without changes in direction.)
I replaced it with a chinese 100mm K11 chuck on a 1:50 harmonic drive.
Nothing difficult here except to source these damn chinese plugs used in the YOOCNC.

Status: DONE

A axis end stop

I wanted a homing switch on the 4th axis too. So I designed a mount for an inductive switch and a way to trigger it using a washer.


3D Touch probe

I got myself a nice Usovo 3D touch probe from the Sorotech shop.
Problem #1 is: It's normally closed while my tool height probe is normally open.
Problem #2 is: When open and supplied with 5V, it still runs at 1.6V while the tool height probe runs at 1.1V. (Both are very imperfect switches)
The PLCM-B1 optocouplers interprete 1.6V as HIGH.

So I'm currently soldering some CMOS NAND gates to
a) Trigger only above 2.5V
b) Combine both probes as NAND(tool heigh, NOT(3D touch probe)) into the same input channel for MACH3.


ATC and compressor

For serveral years I had my eyed on an automatic tool changer from USOVO.
However I could not find silent compressors doing 8 Bar at the low point of hysteresis.

Now I ordered one here.
It is advertised to have 10bar pressure in the tank and provide 8 bar.
...Or so I thought.
That advertisement from Frada-Shop is WRONG.
It starts up at just 5 bar and at 8 bar the safety valve goes off.
The tank (rated at 13 bar) will never, ever reach 10 bar.

Frade-Shop has not reacted with any word about this discrepancy in their advertisement and the delivered product. The only reaction was "your tank is too small".

I'll try to get it to start at more then 5 bar and hope for the pressure-booster that Sorotech wants to announce soon.



One thing I want to add at a very late stage is bellows to protect the Z and Y axis from dust.
Dealers on AliExpress even have some cool looking metal reinforced bellows.


Servo drives

Another upgrade I want to do later is to replace the stepper motors with servo motors.
They have become quite cheap in china lately.